1. Field of the Invention
The present invention relates to a recording/playback apparatus of a helical scanning system. More particularly, it relates to a recording/playback apparatus which is endowed with the function of controlling the contact between a head and a magnetic tape.
2. Description of the Related Art
In a conventional video tape recorder (VTR), a magnetic tape is held at a stop in the state in which the tape is wound on a rotary head, when in a standby mode such as during the pause of playback or picture recording. Moreover, during the standby mode, the rotary head is kept rotating steadily in order to restart the playback or picture recording operation quickly when the pause has been released or canceled.
Also in a conventional data streamer, during a standby for the transfer of data from a host computer, a head is kept rotating in the state in which a magnetic tape at a stop is wound round a rotary head device, in order that the data may be recordable as soon as the standby has ended.
In this manner, while the conventional VTR or data streamer is on standby, the tape is kept wound round the rotary head device in the stopped state, and the head is steadily rotating. Therefore, the head continues to slidingly move on the same part of the tape. In consequence, both the head and the tape wear away severely. This situation incurs the problem that the tape part in contact with the head is damaged due to the wear, so the reliability of the recorded data lowers. As another problem, magnetic powder developed by the wear of the tape and the head accumulates around the head and hampers the normal operation of the head, so the apparatus is prone to going out of order.
With the intention of relieving such problems incurred between the head and the tape, there has been proposed a method wherein the tension of the tape is temporarily relaxed. Also proposed is a method disclosed in U.S. Pat. No. 3,961,372 wherein a rotary shaft in the rotary head device is hollowed to form an air circulation passage and wherein air is supplied into the rotary head so as to spout the air from the whole of the periphery of the rotary head, whereby the tape is entirely floated away from the rotary head to become out of contact with the head.
However, with either of the prior-art methods of relaxing the tape tension temporarily and floating the whole peripheral tape part by the spouting of air, the tape is entirely separated from the rotary head and is slackened. In shifting from the standby mode to the recording or playback mode, therefore, the apparatus needs to wind the tape round the rotary head device again. Consequently, a time period for rewinding the separated tape is required. Moreover, in the case where the tape once slackened by the separation is wound again, it is difficult to bring the head back into precise contact with the end point of the data recorded on the tape before the separation. Therefore, a time period for seeking the end point of the recorded data is required after the tape has been rewound. In this manner, the prior-art method of relaxing the tape tension or floating the tape part at the whole periphery of the rotary head by the spouting of the air has the problem that a long restarting time is expended in shifting from the standby mode to the subsequent recording/playback mode. Further, the prior-art method has the problem that the tape slackened in the standby state comes off tape guides for the rotary head and sags until the edges thereof damage due to rubbing against the tape guides.
The present invention has for its object to provide a recording/playback apparatus which can prevent the wear of a rotary head and the damage of a magnetic tape in the standby state of rotating the head with the tape wound on the head, and which can record or play back data immediately after the standby.